柴油蜡晶的理论形态预测与显微实际形态的比较

COMPARISON OF THEORETICAL PREDICTION WITH PRACTICAL MORPHOLOGY OF WAX IN DIESEL FUEL

采用BFDH模型和AE模型预测柴油中蜡晶的理论形态,与通过相衬光学显微镜在冷环境平台上观察柴油蜡晶在低温下析出的实际形态,以及加入低温流动性改进剂T1804的柴油蜡晶形态进行比较研究。以十八烷晶体和二十三烷晶体作为柴油蜡晶中偶数正构烷烃和奇数正构烷烃的模型化合物,得到它们的晶体理论形态为六面体薄片状晶体。不同降温速率下得到的蜡晶的实际形态与大小均不同。快速降温条件下得到的晶体形态主要为六边形、菱形和其它少数不规则多边形薄片状集合体;慢速降温条件下得到的柴油蜡晶的形态比较完整,为六边形片状,与通过BFDH和AE模型得到的十八烷即偶数正构烷烃的形态比较接近。柴油加T1804后,快速降温时,出现更多细小的无规则晶体,且很快聚集成片状晶体;慢速降温时,出现晶体的数目要多于未加剂柴油,形状不规则,且尺寸小于未加剂柴油。

The theoretical shapes of the wax in the diesel fuel were predicted according to BFDH and the attachment energy model （AE） in order to compare them with the practical morphologies of the crystallized wax in the low temperature observed by optical phase contrast microscope. The practical morphologies of wax in diesel after adding cold improver T1804 was also observed. By using n-octadecane and n-tircoane as model compounds of alkanes with even carbon number and odd carbon number respectively, it was demonstrated that the theoretical shapes of n-octadecane and n-tircoane predicted by BFDH model and AE model were hexahedron flake. It could be seen from the theoretical shape that the visible planes of the nocatdecane were （001）, （010）, （101） and （111）, and the visible planes of n-tricosane were （002）, （100）, （110） and （111）. The practical morphology observed by the microscope showed that the shape and size of wax were different in the different cooling speeds. The wax was of hexagon, rhombus, anomalous polygon and some fibriform shape by rapidly cooled treatment, and of hexagon in slow cooling, exhibiting similarity with the theoretical shape of n-octadecane by BFDH and AE. After adding additive T1804, more smaller anomalous crystals could be observed and aggregated fast into flake crystal.